Georgia State Sea Shell

Knobbed Whelk

(Busycon carica gmelin)

Adopted in 1987

Christened the state seashell in 1987, the knobbed whelk is a whorled shell, eight inches long at maturity, displaying heavy spines, many knobs, and an orange or red mouth. Minerals in Georgia coastal waters cause ocher striations on the sand-colored, semi-gloss surface. This marine snail shell is found all along Georgia's shoreline, out to 30 feet of water.

The Knobbed Whelk, also known as the conch shell. Busycon carica was described by Gmelin in 1791. It is one of approximately fourteen recognized species (depending on how you fell about subspecies and forms) of the subfamily Bucyconinae, in the family Melongenidae. This subfamily has been a conspicuous component of the marine gastropod fauna of eastern North America through most of the Cenozoic. Whelks have flourished in this region of the Atlantic Ocean since the lower Miocene (approximately 30 million years ago). Today the Knobbed Whelk is a common predator of the intertidal mudflats, and can be found offshore to 26 fathoms.

Shell Character

The Knobbed Whelk has a spiral shell with knobs (or spines) along its shoulder. The whelk's mantle, a thin layer of tissue located between the body and the shell, creates the shell. The whelk builds the hard shell from calcium carbonate that it extracts from the seas. The shell is light gray to tan, and often has brown and white streaks. Knobbed whelks grow to eight or nine inches in shallow water along the coast from Massachusetts to northern Florida. Where they are often a conspicuous gastropod of the bays and estuaries. These animals begin life as small, ~4mm long, crawling snails. Each individual is either male or female, and reach maturity in 3 to 5 years. An adult female will be much larger than a male of the same age.

Anatomy

The soft body is divided into the head, the visceral mass, and the foot (which is small). The Knobbed Whelk has two pairs of tentacles on the head; it has a light-sensitive eyespot located on each of the larger tentacles. The smaller pair of tentacles is used for the sense of smell and the sense of touch.

Diet

Like lightning whelks, knobbed whelks feed on clams, and the females lay strings of egg capsules attached by one end in the sand. They will use their shell's lip to chip and pry the valves of their prey apart. Once there is sufficient room, they insert their proboscis and begin feeding. This method of feeding causes a significant amount of damage the shell, and may account for the limited growth of adult shells. Instead of growing, they must spend their time and energy repairing their shells. In intertidal waters, the snails are active throughout the day.
 

Reproduction

Twice a year in the southern part of their range (April-May and September-October in Georgia) and once a year in the north, the snails gather in the estuaries to mate. After mating the female will remain to lay an egg case.

Whelk eggs resemble a telephone cord but actually consist of a number of separate capsules attached to a "string". Each capsule may contain from 0-20 eggs depending on the species of whelk and the location of the capsule on the string. Frequently the first 5-15 capsules are empty, with the number of eggs per subsequent capsule increasing toward the end of the string. Since the beginning of the string is buried in the substrate as an anchor and the eggs may not be able to survive under the substrate, the female may be conserving energy by not placing eggs into these capsules. Energy conservation is very important at this stage in the female's life; laying a string of over 100 capsules may take days to produce! This process can be very strenuous to the female!

Most marine mollusks have external fertilization of eggs in the water column, followed by a planktonic larval development phase. However, when the female whelk deposits egg capsules, the embryos inside are already fertilized. This is because fertilization is internal in these species of whelks. This makes them unique compared to most mollusks in that the young hatch out of these capsules as fully formed juveniles.

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